1. Field of the Invention
The present invention relates to a circuit for automatically closing an interrupted remote feed loop, and in particular to a means for automatically closing the interrupted loop in front of the interrupt location in a remote feed loop for a means for supplying electrical users with DC series current.
2. Description of the Prior Art
A circuit is described in Siemens Zeitschrift 48 (1974) supplement "Nachrichten-Ubertragungstechnik", at page 111 (particularly FIG. 5) for automatically closing an interrupted remote feed loop in front of the interrupt location. This circuit includes a series arm having a holding winding of a switching relay and a response winding which can be switched on given non-actuation of the relay, and which can be swtiched off given actuation of the relay. The relay also has a cross or shunt arm having a break contact, a choke, and a series connection including a resistor. The relay is actuated by current flowing in the remote feed loop which is a fraction of the rated value of the remote feed current. The relay changes state given a reduction of the remote feed current below a prescribed value. An RC connection is connected in parallel with the break contact.
Remote current supplied intermediate regenerator locations or repeater locations for a long distance communication system may contain so-called switch auxiliaries which perform the function of re-closing the remote feed circuit in front of the faulty repeater field in case of a line interruption. Location of the site of the fault can then be undertaken by any known fault locating method included within the system.
For this purpose, it is known from the above publication to employ switching relays having a break contact in the switch auxiliaries, the coil of the switching relay being traversed in normal operation by the remote feed current which maintains the contact open. In the event of a line interruption, the contact closes and connects both remote feed current paths to one another. The contact is in the form of a change-over contact having an off side which switches the cross or shunt connection and having a working side which, after response of the switching relay, shorts a portion of the excitation winding of the relay serving as a response winding, so that only a portion of the winding, serving as a holding winding, is then still effective.
In such a conventional switch auxiliary, the holding voltage drop at the relay coil must be significantly lower than the operating voltage of the regenerator or repeater, which in practice requires response powers of, for example, less than 100 mW.
A high remote feed voltage of, for example, 1200 volts may be continuously adjacent between the opened contacts. When closing, the section capacitances charged to this voltage, which may be on the order of several microfarads, must be able to discharge. At the other extreme, even after years of non-actuation, the contacts must reliably close even at low voltages of, for example, less than 20 volts.